Radio communication base station apparatus in multiple-carrier communication and radio communication method

ABSTRACT

A base station is provided to suppress a drop of receiving power and deterioration of receiving characteristics by cancellation between the same symbols in the case of application of a repetition technology to multiple-carrier communication. In this base station ( 100 ), a repetition unit ( 103 ) for reproducing (making repetition of) each data symbol input from a modulating unit ( 102 ) to make out a plurality of identical data symbols, and a phase rotating unit ( 106 ) for giving a phase rotation to a data symbol input from a multiplexing unit ( 105 ). This time the phase rotating unit ( 106 ) provides the identical symbols made out by the repetition with the phase rotation which has a phase rotating difference different from phase rotating differences among a plurality of identical symbols transmitted with the ones identical to a plurality of the identical symbols at time and a frequency identical to those of a plurality of the identical symbols in adjacent cells or adjacent sectors.

TECHNICAL FIELD

The present invention relates to a radio communication base stationapparatus and radio communication method in multicarrier communication.

BACKGROUND ART

Recently, in radio communication, particularly, in mobile communication,various information such as images and data other than speech aretransmission targets. It is anticipated that demands for higher-speedtransmission will increase in the future, and a radio transmittingtechnique for realizing high transmission efficiency utilizing limitedfrequency resources more efficiently to perform high-speed transmissionis demanded.

OFDM is one of radio transmitting techniques to meet these demands. OFDMis a multicarrier transmitting technique for transmitting data inparallel using a plurality of subcarriers, and is known to have featuresof realizing high frequency efficiency and reducing inter-symbolinterference under multipath environment and be effective for improvingtransmission efficiency.

Further, OFDM provides the maximum frequency efficiency in multicarriercommunication because the frequencies of a plurality of subcarriers inwhich data is arranged are orthogonal to each other, and enablesmulticarrier communication with a comparatively simple hardwareconfiguration. For this reason, OFDM is focused upon as a communicationmethod to be employed in cellular scheme mobile communication andvarious studies upon this communication are underway. Further, withOFDM, to prevent inter-symbol interference (ISI), the rear portion of anOFDM symbol is added to the head of the OFDM symbol as a cyclic prefix(CP). Consequently, the receiving end is able to prevent ISI as long asthe delay time of the delay wave stays within the time length of the CP(hereinafter simply “CP length”).

Furthermore, with OFDM, quality varies significantly between subcarriersdue to frequency selective fading resulting from multipath. In thiscase, given that a signal allocated to a subcarrier in a location whichis a valley of fading has poor quality and makes demodulation difficult,it is necessary to improve quality such that demodulation is possible.

There is a repetition technique as a technique for improving quality inOFDM. The repetition technique is directed to performing transmission bygenerating a plurality of the same symbols by repeating (i.e.repetition) a certain symbol and allocating a plurality of the samesymbols to a plurality of different subcarriers or different times, sothat the receiving end is able to obtain diversity gain by performingmaximum ratio combining of these same symbols (see, for example,Non-Patent Document 1).

On the other hand, transmission diversity techniques which are effectiveto reduce inter-cell interference include a technique of transmittingthe same symbol at the same time, by the same frequency, from the radiocommunication base station apparatuses (hereinafter “base stations”) ofa plurality of cells. As a result of such transmission, a radiocommunication mobile station apparatus (hereinafter “mobile station”)located near the cell edge receives mixed same symbols from a pluralityof base stations. Consequently, in cases where OFDM is applied to thistransmission diversity technique, in the mobile station located near thecell edge, inter-cell interference is not produced as long as aplurality of the same OFDM symbols transmitted from a plurality of basestations at the same time are received with a time lag within the rangeof the OP length, and these OFDM symbols are combined and received asOFDM symbols with amplified transmission power, so that it is possibleto obtain diversity gain.

Non-Patent Document 1: “Performance Comparisons between OFCDM and OFDMin a Forward Link Broadband Channel,” Noriyuki MAEDA, Hiroyuki ATARASHI,Yoshihisa KISHIYAMA, Mamoru SAWAHASHI, The Institute of Electronics,Information and Communication Engineers, TECHNICAL REPORT OF ISICE,RCS2002-162, August 2002, pp. 95 to 100

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

A case will be described here where radio communication that combinesthe above techniques is performed in the mobile communication systemshown in FIG. 1. That is, in this mobile communication system, the basestation in cell A (BS_(A)) and the base station in cell B (BS_(B)) bothtransmit the same OFDM symbols (OFDM symbol A and OFDM symbol B)comprised of subcarriers of the same frequency, to a mobile station (MS)at the same time. OFDM symbol A and OFDM symbol B are each formed withsubcarriers f₁ to f₄ as shown in FIG. 2. Further, in base station BS_(A)and base station BS_(B), the same data symbols S₁ and S₁′ (S₁′ is a datasymbol which is generated by repeating S₁ and which is the same as S₁;the same applies below) are allocated to subcarriers f₁ and f₃, and thesame data symbols S₂ and S₂′ are allocated to subcarriers f₂ and f₄.

In this case, as shown in FIG. 3, if S₁ and S₁′ in cell A and S₁ and S₁′in cell B are each received in the mobile station with out of phase dueto the influence of channel variation in the channels, given that S₁scancel each other and S₁′s cancel each other, the received power of bothS₁ and S₁′ decrease significantly and diversity gain resulting fromcombination of S₁ and S₁′ cannot be obtained, which results indegradation of received performances. Further, FIG. 3 shows a case wherethe phases of S₁ and S₁′ in cell B rotate 180 degrees in the channels.

It is therefore an object of the present invention to provide a basestation and radio communication method that, in cases where therepetition technique is employed in multicarrier communication, make itpossible to prevent reduction in received power resulting fromcancellation between the same symbols and prevent degradation ofreceived performances.

Means for Solving the Problem

The base station according to the present invention that transmits amulticarrier signal comprised of a plurality of subcarriers to a radiocommunication mobile station apparatus, includes: a repetition sectionthat repeats a first symbol to generate a plurality of same firstsymbols; a phase rotation section that applies a phase rotation to theplurality of first symbols; and a transmitting section that transmitsthe multicarrier signal in which the plurality of first symbols givenphase rotations are allocated to the plurality of subcarriers, andemploys a configuration in which the phase rotation section makes aphase rotation difference produced between the plurality of firstsymbols different from a phase rotation difference produced between aplurality of second symbols which are the same as the plurality of firstsymbols and which are transmitted in adjacent cells or adjacent sectorsat the same time, by the same frequency, as the plurality of firstsymbols.

ADVANTAGEOUS EFFECT OF THE INVENTION

The present invention makes it possible to prevent reduction in receivedpower resulting from cancellation between the same symbols and preventdegradation of received performances in cases where the repetitiontechnique is employed in multicarrier communication.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows cell arrangement of a two-cell model;

FIG. 2 shows a data symbol after repetition;

FIG. 3 shows a data symbol influenced by channel variation;

FIG. 4 is a block diagram showing a configuration of a base stationaccording to an embodiment of the present invention;

FIG. 5 is a block diagram showing a configuration of a mobile stationaccording to an embodiment of the present invention;

FIG. 6 illustrates phase rotation according to an embodiment of thepresent invention (cell A);

FIG. 7 illustrates phase rotation according to an embodiment of thepresent invention (cell B);

FIG. 3 illustrates phase rotation according to an embodiment of thepresent invention (cell A);

FIG. 9 illustrates phase rotation according to an embodiment of thepresent invention (cell B);

FIG. 10 shows a data symbol according to an embodiment of the presentinvention (cell A);

FIG. 11 shows a data symbol according to an embodiment of the presentinvention (cell B);

FIG. 12 shows a received symbol according to an embodiment of thepresent invention;

FIG. 13 shows a received symbol according to an embodiment of thepresent invention;

FIG. 14 shows a received symbol according to an embodiment of thepresent invention;

FIG. 15 shows a received symbol according to an embodiment of thepresent invention;

FIG. 16 shows cell arrangement according to an embodiment of the presentinvention (three-cell model);

FIG. 17 illustrates phase rotation according to an embodiment of thepresent invention (cell B);

FIG. 18 illustrates phase rotation according to an embodiment of thepresent invention (cell C);

FIG. 19 shows sector arrangement according to an embodiment of thepresent invention (three-sector model);

FIG. 20 is a block diagram showing a configuration of the base stationaccording to an embodiment of the present invention (three-sectormodel);

FIG. 21 illustrates phase rotation according to an embodiment of thepresent invention (cell A); and

FIG. 22 illustrates phase rotation according to an embodiment of thepresent invention (cell B).

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail belowwith reference to the drawings.

With the present embodiment, the base station applies phase rotations toa plurality of the same symbols generated by repetition such that thephase rotation differences produced between a plurality of the samesymbols are different from the phase rotation differences producedbetween a plurality of the same symbols transmitted in adjacent cells oradjacent sectors at the same time, by the same frequency as a pluralityof the same symbols generated by repetition.

FIG. 4 shows a configuration of base station 100 according to thepresent embodiment. With the present embodiment, base station BS_(A) andbase station BS_(B) shown in FIG. 1 both employ a configuration shown inFIG. 4.

In base station 100, encoding section 101 carries out encodingprocessing of inputted transmission data (bit sequence), and modulatingsection 102 generates a data symbol by carrying out modulationprocessing of the encoded transmission data by the modulation schemesuch as QPSK and 16QAM.

Repetition section 103 generates a plurality of the same data symbols byrepeating (i.e. repetition) each data symbol inputted from modulatingsection 102, and outputs a plurality of the same data symbols to S/Psection (serial-to-parallel converting section) 104. In the followingdescription, a plurality of the same data symbols will be referred to asthe “unit of repetition.”

S/P section 104 converts, into parallel, the data symbol sequenceinputted from repetition section 103 in a series, and outputs the datasymbol sequence to multiplexing section 105. By means of thisserial-to-parallel conversion, each data symbol is allocated to aplurality of subcarriers forming a multicarrier signal.

Multiplexing section 105 time-domain-multiplexes the data symbols andthe pilot symbols by selecting and outputting a pilot symbol each time apredetermined number of data symbols (for example, one frame of datasymbols) are inputted from S/P section 104.

Phase rotation section 106 applies phase rotations to the data symbolsinputted from multiplexing section 105. The phase rotation will bedescribed in detail later. The data symbols given phase rotations areoutputted to IFFT (Inverse Fast Fourier Transform) section 107.

IFFT section 107 performs an IFFT of a plurality of subcarriers to whichthe pilot symbols or data symbols are allocated, to acquire an OFDMsymbol which is a multicarrier signal.

CP adding section 108 provides a CP by adding the same signal as therear portion of an OFDM symbol, to the head of the OFDM symbol.

Radio transmitting section 109 carries out transmission processing suchas D/A conversion, amplification and up-conversion of the OFDM symbolafter the CP is added, and transmits the result to the mobile stationshown in FIG. 5 from antenna 110.

Next, FIG. 5 shows a configuration of mobile station 200 according tothe present embodiment. Mobile station MS shown in FIG. 1 employs theconfiguration shown in FIG. 5.

In mobile station 200, the OFDM symbol received through antenna 201 issubjected to reception processing such as down-conversion and A/Dconversion in radio receiving section 202, is removed the CP in CPremoving section 203 and is inputted to FFT (Fast Fourier Transform)section 204.

FFT section 204 extracts the symbol allocated to each subcarrier byperforming an FFT of the OFDM symbol, and outputs one OFDM symbol tochannel compensating section 205.

Channel compensating section 205 calculates a channel estimation valueof each subcarrier by performing channel estimation using the receivedpilot symbol, and compensates for the channel variation of the datasymbols based on this channel estimation value. In this case, channelcompensating section 205 calculates a channel compensation value takinginto account the phase rotation applied in base station 100. One OFDMsymbol of the data symbols after channel variation compensation isoutputted in parallel, to P/S section 206.

P/S section 206 converts the data symbol sequences inputted in parallelfrom channel compensating section 205 into a series, and outputs theresult to combining section 207.

Combining section 207 combines the data symbols in repetition units,that is, between the same data symbols generated by repetition in basestation 100.

Further, the operations of channel compensating section 205 andcombining section 207 will be described in detail.

The combined symbol is demodulated in demodulating section 208 and isdecoded in decoding section 209. By this means, received data can beobtained.

Next, the phase rotation applied in phase rotation section 106 of basestation 100 and the operations of channel compensating section 205 andcombining section 207 of mobile station 200 will be described in detail.

First, a case will be described where there is one cell, cell B,adjacent to cell A, as shown in FIG. 1. In the following description, asdescribed above, OFDM symbol A and OFDM symbol B are each formed withsubcarriers f₁ to f₄. Further, in the base station in cell A (BS_(A))and the base station in cell B (BS_(B)), the same data symbols S₁ andS₁′ are allocated to subcarriers f₁ and f₃, and the same data symbols S₂and S₂′ are allocated to subcarriers f₂ and f₄. Then, base stationBS_(A) and base station BS_(B) both transmit the same OFDM symbols (OFDMsymbol A and OFDM symbol B) comprised of subcarriers of the samefrequency to a mobile station (MS) at the same time. Further, althoughthe following description focuses upon data symbol S₁ and S₁′, as todata symbols S₂ and S₂′, the present invention can be implemented in thesame way.

As shown in FIG. 6, base station BS_(A) applies phase rotations of phaserotation angles φ_(A1) and φ_(A3) to the same data symbols S₁ and S₁′.In this way, the phase rotation difference between S₁ and S₁′ in cell Ais Δφ_(A)=φ_(A3)−φ_(A1).

On the other hand, as shown in FIG. 7, base station BS_(B) applies phaserotations of phase rotation angles φ_(B1) and φ_(B3), to the same datasymbols S₁ and S₁′. In this way, the phase rotation difference betweenS₁ and S₁′ in cell B is Δφ_(B)=φ_(B3)−φ_(B1).

Further, with the present invention, Δφ_(A)≠Δφ_(B). That is, with thepresent invention, the phase rotation difference Δφ_(A) between the datasymbols S₁ and S₁′ in cell A and the phase rotation difference Δφ_(B)between the data symbols S₁ and S₁′ in cell B, adjacent to cell A, aredifferent.

For example, as shown in FIG. 8 and FIG. 9, Δφ_(A)=0 degree assumingthat φ_(A1)=0 degree and φ_(A3)=0 degree, and Δφ_(B)=180 degreesassuming that φ_(B1)=0 degree and φ_(B3)=180 degrees. In this way, S₁and S₁′ included in OFDM symbol A transmitted from base station BS_(A)in cell A are as shown in FIG. 10, and S₁ and S₁′ included in OFDMsymbol B transmitted from base station BS_(B) in cell B are as shown inFIG. 11. OFDM symbol A and OFDM symbol B including S₁ and S₁′, to whichsuch phase rotations are applied, are received by mobile station MS.

FIG. 12 shows the received symbol in mobile station MS. Data symbolsreceived by means of subcarriers f₁ and f₄ are data symbols R₁ to R₄. R₁and R₃ received by means of subcarriers f₁ and f₃ to which S₁ and S₁′are allocated, will be focused upon and described. Further, in thefollowing description, the channel variation in subcarrier f₁ in cell Ais h_(A1), the channel variation in subcarrier f₃ in cell A is h_(A3),the channel variation in subcarrier f₁ in cell B is h_(B1) and thechannel variation in subcarrier f₃ in cell B is h_(B3). Furthermore,assuming that the frequency interval between subcarriers f₁ and f₃ isnarrow and these subcarriers stay in the coherent bandwidth, frequencyperformances in the channels are uniform between subcarriers f₁ and f₃,so that h_(A1)=h_(A3) and h_(B1)=h_(B3). Still further, assuming thatsubcarriers f₁ and f₃ stay in the coherent bandwidth, Δφ_(A) applied inbase station BS_(A) and Δφ_(B) applied in base station BS_(B) aremaintained as is until Δφ_(A) and Δφ_(B) reach to mobile station MS.

Three cases of (1) h_(A1)=h_(A3)=90 degrees and h_(B1)=h_(B3)=180degrees, (2) h_(A1)=h_(A3)=90 degrees and h_(B1)=h_(B3)=270 degrees, and(3) h_(A1)=h_(A3)=45 degrees and h_(B1)=h_(B3)=90 degrees, will beassumed and described below.

(1) Case of h_(A1)=h_(A3)=90 degrees and h_(B1)=h_(B3)=180 degrees (FIG.13A to H)

Given that h_(A1)=90 degrees and h_(B1)=180 degrees, the phase of S₁ incell A (FIG. 10) rotates 90 degrees in the channel and the phase of S₁in cell B (FIG. 11) rotates 180 degrees in the channel. In this way, S₁in cell A and S₁ in cell B are combined in channels, so that receivedsymbol R₁ is as shown in FIG. 13A.

Given that h_(A3)=90 degrees and h_(B3)=180 degrees, the phase of S₁′ incell A (FIG. 10) rotates 90 degrees in the channel and the phase of S₁′in cell B (FIG. 11) rotates 180 degrees in the channel. In this way, S₁′in cell A and S₁′ in cell B are combined in the channels, so thatreceived symbol R₃ is as shown in FIG. 13B.

On the other hand, channel estimation values resulting from channelestimation in channel compensating section 205 are h_(A1)=h_(A3)=90degrees and h_(B1)=h_(B3)=180 degrees as shown in FIG. 13C and FIG. 13D.

According to φ_(B3)=180 degrees, channel compensating section 205carries out processing to reverse the phase of h_(B3) in FIG. 13D 180degrees as shown in FIG. 13E. This processing makes h_(B3)=0 degree.

Next, channel compensating section 205 finds combined channel estimationvalue h₁ in subcarrier f₁ by combining h_(A1) and h_(B1) as shown inFIG. 13F, to find the channel estimation value for R₁ obtained bycombining S₁ in cell A and S₁ in cell B. In this way, h₁=135 degrees. Inthe same way, channel compensating section 205 finds combined channelestimation value h₃ in subcarrier f₃ by combining h_(A3) and h_(B3)after the phase is reversed, as shown in FIG. 13G, to find the channelestimation value for R₃ obtained by combining S₁′ in cell A and S₁′ incell B. In this way, h₃=45 degrees.

Next, as shown in FIG. 13H, channel compensating section 205 compensatesfor the channel variation in R₁ based on h₁ and compensates for thechannel variation in R₃ based on h₃. That is, channel compensatingsection 205 carries out processing to reverse the phase of R₁ 135degrees and the phase of R₃ 45 degrees.

Then, as shown in FIG. 13H, combining section 207 combines R₁ and R₃after compensation for channel variation and acquires the combinedsymbol R₁+R₃.

In this way, Δφ_(A)=0 degree and Δφ_(B)=180 degrees, so that it ispossible to prevent S₁ and S₁′ in cell A and S₁ and S₁′ in cell B frombeing received by mobile station MS with out of phase.

(2) Case of h_(A1)=h_(A3)=90 degrees and h_(B1)=h_(B3)=270 degrees (FIG.14A to H)

Given that h_(A1)=90 degrees and h_(B1)=270 degrees, the phase of S₁ incell A (FIG. 10) rotates 90 degrees in the channel, and the phase of S₁in cell B (FIG. 11) rotates 270 degrees in the channel. In this way, S₁in cell A and S₁ in cell B are combined in the channels, so thatreceived symbol R₁ is zero as shown in FIG. 14A.

Further, given that h_(A3)=90 degrees and h_(B3)=270 degrees, the phaseof S₁′ in cell A (FIG. 10) rotates 90 degrees in the channel, and thephase of S₁′ in Cell B (FIG. 11) rotates 270 degrees in the channel. Inthis way, S₁′ in cell A and S₁′ in cell B are combined in the channels,so that received symbol R₃ is as shown in FIG. 14B.

On the other hand, channel estimation values resulting from channelestimation in channel compensating section 205 are h_(A1)=h_(A3)=90degrees and h_(B1)=h_(B3)=270 degrees as shown in FIGS. 14C and D.

According to φ_(B3)=180 degrees, channel compensating section 205carries out processing to reverse the phase of h_(B3) in FIG. 14D 180degrees as shown in FIG. 14E. This processing makes h_(B3)=90 degrees.

Next, channel compensating section 205 finds combined channel estimationvalue h₁ in subcarrier f₁ by combining h_(A1) and h_(B1) as shown inFIG. 14F, to find the channel estimation value for R₁ obtained bycombining S₁ in cell A and S₁ in cell B. In this way, h₁=zero. In thesame way, channel compensating section 205 finds combined channelestimation value h₃ in subcarrier f₃ by combining h_(A3) and h_(B3)after the phase is reversed, as shown in FIG. 14G, to find the channelestimation value for R₃ obtained by combining S₁′ in cell A and S₁′ incell B. In this way, h₃=90 degrees.

Next, as shown in FIG. 14H, channel compensating section 205 compensatesfor the channel variation in R₁ based on h₁ and compensates for thechannel variation in R₃ based on h₃. In this case, given that R₁ iszero, channel compensating section 205 carries out only processing toreverse the phase of R₃ 90 degrees.

Then, as shown in FIG. 14H, combining section 207 combines R₁ and R₃after compensation for channel variation and acquires the combinedsymbol R₁+R₃. Given that R₁ is zero, R₃ can be obtained as the combinedsymbol.

In this way, Δφ_(A)=0 degree and Δφ_(B)=180 degrees, so that it ispossible to prevent S₁ and S₁′ in cell A and S₁ and S₁′ in cell B frombeing received by mobile station MS with out of phase, as in case ofabove (1).

(3) Case of h_(A1)=h_(A3)=45 degrees and h_(B1)=h_(B3)=90 degrees (FIG.15A to H)

Given that h_(A1)=45 degrees and h_(B1)=90 degrees, the phase of S₁ incell A (FIG. 10) rotates 45 degrees in the channel and the phase of S₁in cell B (FIG. 11) rotates 90 degrees in the channel. In this way, S₁in cell A and S₁ in cell B are combined in channels, so that receivedsymbol R₁ is as shown in FIG. 15A.

Given that h_(A3)=45 degrees and h_(B3)=90 degrees, the phase of S₁′ incell A (FIG. 10) rotates 45 degrees in the channel and the phase of S₁′in cell B (FIG. 11) rotates 90 degrees in the channel. In this way, S₁′in cell A and S₁′ in cell B are combined in channels, so that receivedsymbol R₃ is as shown in FIG. 15B.

On the other hand, channel estimation values resulting from channelestimation in channel compensating section 205 are h_(A1)=h_(A3)=45degrees and h_(B1)=h_(B3)=90 degrees as shown in FIG. 15C and FIG. 15D.

According to φ_(B3)=180 degrees, channel compensating section 205carries out processing to reverse the phase of h_(B) 3 in FIG. 15D 180degrees as shown in FIG. 15E. This processing makes h_(B3)=270 degrees.

Next, channel compensating section 205 finds combined channel estimationvalue h₁ in subcarrier f₁ by combining h_(A1) and h_(B1) as shown inFIG. 15F, to find the channel estimation value for R₁ obtained bycombining S₁ in cell A and S₁ in cell B. In this way, h₁=67.5 degrees.In the same way, channel compensating section 205 finds combined channelestimation value h₃ in subcarrier f₃ by combining h_(A3) and h_(B3)after the phase is reversed, as shown in FIG. 15G, to find the channelestimation value for R₃ obtained by combining S₁′ in cell A and S₁′ incell B. In this way, h₃=337.5 degrees.

Next, as shown in FIG. 15H, channel compensating section 205 compensatesfor the channel variation in R₁ based on h₁ and compensates for thechannel variation in R₃ based on h₃. That is, channel compensatingsection 205 carries out processing to reverse the phase of R₁ 66.5degrees and the phase of R₃ 337.5 degrees.

Then, as shown in FIG. 15H, combining section 207 combines R₁ and R₃after compensation for the channel variation and acquires the combinedsymbol R₁+R₃.

In this way, Δφ_(A)=0 degree and Δφ_(B)=180 degrees, so that it ispossible to prevent S₁ and S₁′ in cell A and S₁ and S₁′ in cell B frombeing received by mobile station MS with out of phase, as in cases ofabove (1) and (2).

As is clear from the above description, Δφ_(A)≠Δφ_(B), so that, evenwhen S₁ and S₁′ are influenced by the phase variation in the channels,it is possible to prevent the received power of both R₁ and R₃ fromdecreasing to zero in the mobile station and prevent R₁ and R₃ frombeing lost, and obtain diversity gain resulting from combination of S₁and S₁′, and, consequently, prevent degradation of receivedperformances.

It is preferable to maximize the phase rotation differences betweenadjacent cells to minimize degradation of received performances due tocancellation between S₁s and between S₁′s.

For example, in the two-cell model shown in FIG. 1, it is preferable tomake the difference between the phase rotation difference Δφ_(A) in cellA and the phase rotation difference Δφ_(B) in cell B 180 degrees, asdescribed above.

Further, in the three-cell model shown in FIG. 16 it is preferable tomake the differences between the phase rotation difference Δφ_(A) incell A, the phase rotation difference Δφ_(B) in cell B, and the phaserotation difference Δφ_(C) in cell C, all 120 degrees. Consequently, forexample, in cases where the phase rotation (Δφ_(A)=0 degree assumingthat φ_(A1)=0 degree and φ_(A3)=0 degree) as shown in FIG. 8 is appliedin cell A, it is preferable that Δφ_(B)=120 degrees assuming thatφ_(B1)=0 degree and φ_(B3)=120 degrees in cell B as shown in FIG. 17 andΔφ_(C)=240 degrees assuming that φ_(C1)=0 degree and φ_(C3)=240 degreesin cell C as shown in FIG. 18.

In this way, with the present embodiment, base stations in cellsadjacent to each other make the phase rotation difference between S₁ andS₁′ a value matching the number of adjacent cells. For example, in thetwo-cell model shown in FIG. 1, there is one cell, B cell, adjacent tocell A and, in the three-cell model shown in FIG. 16, there are twocells adjacent to one cell, so that each base station applies phaserotations φ₁ and φ₃ that produce the phase rotation difference Δφaccording to equation (1), to S₁ and S₁′. For example, in the two-cellmodel, by changing n in equation (1) to n=0 or 1, base station BS_(A)applies phase rotations φ_(A1) and φ_(A3) that produce a phase rotationdifference Δφ_(A) in case of n=0, to S₁ and S₁′ and base station BS_(B)applies phase rotations φ_(B1) and φ_(B3) that produce a phase rotationdifference Δφ_(B) in case of n=1, to S₁ and S₁′. Further, in thethree-cell model, by changing n in equation (1) to n=0, 1 or 2, basestation BS_(A) applies phase rotations φ_(A1) and φ_(A3) that produce aphase rotation difference Δφ_(A) in case of n=0, to S₁ and S₁′, basestation BS_(B) applies phase rotations φ_(B1) and φ_(B3) that produce aphase rotation difference Δφ_(B) in case of n=1, to S₁ and S₁′ and basestation BS_(C) applies phase rotations φ_(C1) and φ_(C3) that produce aphase rotation difference Δφ_(C) in case of n=2, to S₁ and S₁′.Phase rotation difference=n×(360 degrees/(number of adjacent cells+1),where n is an integer  (Equation 1)

Further, although a case has been described with the above descriptionwhere the present invention is implemented between adjacent cells, thepresent invention can be implemented as described above even betweenadjacent sectors in the same cell. For example, in the three-sectormodel shown in FIG. 19, the present invention can be implemented as inthe three-cell model shown in FIG. 16. That is, assuming that cell A issector A, cell B is sector B and cell C is sector C in the abovedescription, the present invention can be implemented as describedabove. However, in cases where the present invention is implementedbetween adjacent sectors, base station BS shown in FIG. 19 makes thephase rotation difference between S₁ and S₁′ a value matching the numberof sectors in one cell. That is, base station BS applies phase rotationsφ₁ and φ₃ that produce the phase rotation difference Δφ according toequation (2), to S₁ and S₁′ in each sector. To be more specific, in thethree-sector model shown in FIG. 19, given that the number of sectors inone cell is “3,” by changing n in equation (2) to n=0, 1 or 2, phaserotations φ_(A1) and φ_(A3) that produce a phase rotation differenceΔφ_(A) in case of n=0, are applied to S₁ and S₁′ in sector A, phaserotations φ_(B1) and φ_(B3) that produce a phase rotation differenceΔφ_(B) in case of n=1, are applied to S₁ and S₁′ in sector B and phaserotations φ_(C1) and φ_(C3) that produce a phase rotation differenceΔφ_(C) in case of n=2, are applied to S₁ and S₁′ in sector C. By sodoing, it is possible to minimize degradation of received performancesdue to cancellation between S₁s and between S₁′s by maximizing the phaserotation differences between adjacent sectors.Phase rotation difference=n×(360 degrees/number of sectors in one cell),where n is an integer  (Equation 2)

Further, FIG. 20 shows the configuration of base station BS of FIG. 19as base station 300. Base station 300 has sector A apparatus 100-A,sector B apparatus 100-B and sector C apparatus 100-C that each have thesame configuration. Sector A apparatus 100-A, sector B apparatus 100-Band sector C apparatus 100-C each have the same configuration as basestation 100 shown in FIG. 4 and receive as input the same transmissiondata.

An embodiment of the present invention has been described above.

Further, the phase rotation may be applied in the base station to S₁ andS₁′ by multiplying S₁ and S₁′ by e^((jθ)). For example, in a case wherethe phase rotation difference in cell A is Δφ_(A)=0, the phase rotationdifference in cell B is Δφ_(B)=e^((jπ)), and the difference betweenΔφ_(A) and Δφ_(B) is e^((jπ)) (that is, 180 degrees), e^((jπ/4)) ismultiplied upon S₁ and S₁′ in cell A as shown in FIG. 21 and e^((j3π/4))is multiplied upon S₁ and e^((j7π/4)) is multiplied upon S₁′ in cell Bas shown in FIG. 22. Further, the phase rotation applied using thismultiplication may be performed by multiplying cell-specific orsector-specific scrambling sequences comprised of e^((jθ)) sequence.Furthermore, in cases where the cell-specific or sector-specificscrambling sequences comprised of e^((jθ)) sequence are determined inadvance and cannot be changed, the scrambling sequences may bemultiplied by changing the arrangement of data symbols according to thescrambling sequence so as to produce the desired phase rotationdifference. Still further, in cases where the scrambling sequence hasbeen multiplied upon S₁ and S₁′, the phase rotation may be applied byfurther multiplying e^((jθ)) upon S₁ and S₁′.

The degree of phase rotation applied to each data symbol may be known inadvance between the base station and the mobile station or may bereported from the base station to the mobile station. For example, thedegree of phase rotation may be reported as control information eachtime the OFDM symbol is transmitted.

Further, although a case has been described with the above descriptionas an example where two same data symbols can be acquired assuming thatthe repetition factor (RF) in repetition section 103 is RF=2, thepresent invention is not limited to RF=2 and may be applied to the casewhere RF is three or more.

Furthermore, although a case has been described with the abovedescription where the present invention is applied to downlink, thepresent invention can be applied to uplink. It is possible to apply thepresent invention to uplink by, for example, providing a plurality oftransmitting apparatuses in a mobile station, carrying out the sameprocessing in a plurality of transmitting apparatuses as in basestations 100 and 300 and carrying out the same processing in the basestation as in above mobile station 200.

Further, although a case has been described with the above descriptionwhere the channel estimation value in cell A is found from the pilot incell A, the channel estimation value in cell B is found from the pilotin cell B, and then the combined channel estimation value is found bycombining these channel estimation values, the combined channelestimation value may be found by the following method. That is, the basestation may apply the phase rotation with the same angle as the datasymbol to the pilot in cell A and the pilot in cell B and transmit thesepilots to the mobile station at the same time, by the same frequency,and the mobile station may find the combined channel estimation valuedirectly from the combined received pilot in the channel.

Further, although a case has been described with the above descriptionwhere the present invention is implemented for symbols arranged on thefrequency axis (i.e. frequency domain), the present invention can bealso implemented as described above for symbols arranged on the timeaxis (i.e. time domain).

Although OFDM has been described with the above description as anexample of multicarrier communication, the present invention can beimplemented in multicarrier communication other than OFDM.

Further, the base station, mobile station and subcarrier may be referredto as “Node B,” “UE” and “tone,” respectively. Furthermore, a CP may bereferred to as “guard interval (GI).”

Also, although cases have been described with the above embodiments asexamples where the present invention is configured by hardware, thepresent invention can also be realized by software.

Each function block employed in the description of the above embodimentmay typically be implemented as an LSI constituted by an integratedcircuit. These may be individual chips or partially or totally containedon a single chip. “LSI” is adopted here but this may also be referred toas “IC,” “system LSI,” “super LSI,” or “ultra LSI” depending ondiffering extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of a programmableFPGA (Field Programmable Gate Array) or a reconfigurable processor whereconnections and settings of circuit cells within an LSI can bereconfigured is also possible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2006-128258, filed onMay 2, 2006, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, a mobilecommunication system.

1. A radio communication base station apparatus that transmits amulticarrier signal comprised of a plurality of subcarriers to a radiocommunication mobile station apparatus, the radio communication basestation apparatus comprising: a repetition section that repeats a firstsymbol to generate a plurality of same first symbols; a phase rotationsection that applies a phase rotation to the plurality of first symbols;and a transmitting section that transmits the multicarrier signal inwhich the plurality of first symbols given phase rotations are allocatedto the plurality of subcarriers, wherein the phase rotation sectionmakes a phase rotation difference between the plurality of first symbolsdifferent from a phase rotation difference between a plurality of secondsymbols which are the same as the plurality of first symbols and whichare transmitted in a different cell or a different sector at the sametime, by the same frequency, as the plurality of first symbols.
 2. Theradio communication base station apparatus according to claim 1, whereinthe phase rotation section applies the phase rotation that produces aphase rotation difference matching a number of different cells ordifferent sectors.
 3. The radio communication base station apparatusaccording to claim 1, wherein the phase rotation section applies thephase rotation that produces a phase rotation difference represented byn×(360 degrees/(number of different cells+1)) or a phase rotationdifference represented by n×(360 degrees/number of sectors in one cell),where n is an integer.
 4. The radio communication base station apparatusaccording to claim 1, wherein the phase rotation section makes the phaserotation difference between the plurality of first symbols differentfrom a phase rotation difference between the plurality of second symbolsby multiplying the plurality of first symbols by a scrambling code thatapplies phase rotation that produces a phase rotation differencedifferent from the phase rotation difference between the plurality ofsecond symbols, to the plurality of first symbols.
 5. A radiocommunication method used in a radio communication system where samesymbols are transmitted at the same time, by the same frequency betweena plurality of cells or between a plurality of sectors, the radiocommunication method comprising making a phase rotation differencebetween of the same symbols in a first cell or a first sector differentfrom a phase rotation difference between the same symbols in a secondcell, different from the first cell, or a second sector, different fromthe first sector.